To date, the semiconductor lithography technology has contributed to miniaturization, high integration, and cost reduction by light-based photoengraving. Based on the principle that resolution is improved as optical wavelength becomes shorter, light wavelength has become shorter and shorter with the progress of miniaturization, and there has been a transition from g ray (a wavelength of 436 nm) to i ray (a wavelength of 365 nm), and, at present, excimer laser light having a wavelength of 193 nm is used. Lithography technology using extremely short ultraviolet ray (EUV) having a further shorter wavelength, a wavelength of 13.5 nm, has continued to be developed aggressively.
However, in light-based photoengraving, a mask equivalent to a negative is required without exception. With the advance of miniaturization of semiconductors, the cost of the development of masks has continued to increase, reaching as much as several million yen per type of LSI. Meanwhile, the electron beam drawing device has been used in the development of the masks due to its feature of having a pattern generating function. However, with the advance of optical lithography technology, processing time has increased due to the introduction of super-resolution technology which realizes transcription at a degree of optical wavelength or smaller and the increased amount of mask data generated in association with the high integration. As a result, processing time of drawing a mask needs dozens of hours per single layer of a mask.
As such, for the purposes of reducing the escalating cost of masks through reduction of processing time of drawing a mask and realizing direct drawing by an electron beam drawing device without expensive masks, there has been proposed a multibeam device employing a plurality of electron beams, in order to improve the processing capacity of the electron beam drawing device per unit time. There has been demand for achieving processing capacity which is more than dozens of times the current processing capacity.
There are basically two methods of generating a plurality of electron beams. The first method is a split-and-shape type in which only a single electron gun is used and electrons output from the electron gun are caused to pass through a structure (splitter) having numerous holes, thereby shaping them into a plurality of electron beams, while the second method is of a multiple electron gun type in which an electron gun is provided for each electron beam performing exposure processing.
In the electron beam splitting and shaping drawing method, because the intervals in the splitter are of the order of micrometers, it is impossible to control the strength of the electron beams entering the respective holes to render them uniform and perform adjustment of an axis and determination of a deflection position for each split electron beam, and therefore, there is adopted a scheme in which a single electron optical lens barrel (column) is employed for a plurality of electron beams and only on and off of the electron beams is controlled separately to obtain drawing patterns. However, this scheme has a disadvantage in that the strength of the individual split beams cannot be adjusted with the accuracy required for drawing, and therefore, it is impossible to perform drawing with a high degree of accuracy.
Further, because electrons of beams in a single column have the same negative charge, the electron repulsion phenomenon occurs due to Coulomb repulsive force if the total amount of electrons is large, and beam defocus becomes prominent. Therefore, the amount of available electrons must be limited to, for example, several microamperes. Multibeam technology has also drawn attention as a technology for overcoming this limitation of the processing capacity per electron beam.
Meanwhile, in the multiple electron gun type, because the size of an electron gun is from one to two centimeters, and because a plurality of electron optical lens barrels (referred to as columns) are provided independently for the respective electron beams, this type is referred to as a multicolumn system and has a structure composed of a bundle of dozens of single element columns.
In the multicolumn system, because it is possible to individually control parameters that affect drawing accuracy, such as the strength of a beam, a radiation angle, and current density, it is easy to perform drawing accurately. Because there are a plurality of independent columns, it is possible to perform exposure using an electron beam of greater than or equal to several dozen microamperes in total, and therefore, it is possible to dramatically improve processing capacity and expose several dozens of silicon wafers per hour, even if the total power of electron beams is limited to several microamperes in response to beam defocus due to Coulomb repulsive force.
The conventional electron beam drawing device employing a single column has a processing capacity of 0.1 to 0.2 sheets per hour. In order to realize a processing capacity of 10 to 20 sheets per hour by the multicolumn system in which a plurality of columns are arranged in parallel, it is necessary to arrange approximately 100 columns in a 300 mm wafer. In this case, it is necessary to arrange the columns in rectangular or square-shaped lattice coordinates. For example, it is necessary to arrange 132 or 120 of columns in a 300 mm circle if a single cell is a square lattice of 25 mm. The required number of multiple columns is based on the demand for the processing capacity.
In order to place the columns at pitches of approximately 25 mm, the thickness of a single column has to be smaller than or equal to approximately 25 mm at maximum. This means that the electron lens has to have a diameter smaller than or equal to approximately 23 mm at maximum.
There are electrostatic-type electron lenses and electromagnetic-type electron lenses. It is easy to manufacture an electrostatic electron lens having a diameter smaller than or equal to 23 mm. Further, electrostatic lenses are suitable for the multicolumn system, as potentials of all lenses are easy to match. However, the electrostatic lenses are not suitable to constitute the electron beam drawing device. This is because the electron beam drawing device frequently uses an electrostatic deflector for the reason that the electrostatic deflector can deflect electron beams at high speed. An electromagnetic deflector available as another deflector option is rarely used in a high-speed drawing device because the deflector takes a long time to switch positions of an electron beam due to the problems of eddy current and inductance.
In the electron beam drawing device which frequently uses a high-speed electrostatic deflector, electric field interference tends to occur between the electrostatic deflector and the electrostatic lens, and the axial symmetry of the lens electric field tends to be easily lost. Therefore, it is impossible to form beams accurately by the lens. In order to avoid this, it is necessary to separate the electrostatic deflector sufficiently far from the electrostatic lens along the beam axis direction. For these reasons, it is impossible to use the electrostatic lens in the drawing device in which the distance between the electrostatic deflector and the electrostatic lens is short. If the distance between the electrostatic deflector and the electrostatic lens becomes longer, a column becomes longer and beam defocus increases due to Coulomb repulsive force, and therefore, it is necessary to limit the upper limit of the total power of available electron beam to be small. Therefore, the processing capacity of the electron beam drawing device becomes smaller. As such, it is impossible to use the electrostatic lens in the electron beam drawing device which aims at high speed wafer drawing processing.
Because of the reasons described in the above section, it is essential to use the electromagnetic lens as the electron lens, in order to enhance processing capacity. In the electron beam drawing device, the electromagnetic lens employing an electromagnet has been used. However, if, in the multicolumn system, the number of columns increases from a few to more than several dozen columns, a large amount of Joule heat is generated by a current flowing in the electromagnet, and a vast amount of power from several hundred W to several kW is generated. Such a multicolumn system is unrealistic.
Here, use of a permanent magnet in place of the electromagnet is considered. However, only using the permanent magnet is not enough to make an electron lens suitable for the multicolumn system. Although, generally, strong permanent magnets employing rare earth elements such as samarium cobalt and neodymium are now available as permanent magnets, they tend not to be polarized uniformly and therefore are not easily used in an electron lens which needs to be axially symmetric in a uniform manner. The conventional publicly-known examples employ, for example, as shown in Patent Document 1 and FIG. 5, a ring-shaped permanent magnet which has a large radius and is located apart from the axis inside the pole piece having a large circumference. In most cases, an electron lens magnetic pole gap between pole pieces made of a ferromagnetic material is brought sufficiently closer to the beam axis. In doing so, it is possible to smooth the non-uniformity of permanent magnet by the ferromagnet to thereby form a lens magnetic field having sufficient axial symmetry in the vicinity of the pole piece.
However, with the electron lens employing the permanent magnet having the above-described shape, it is impossible to form a lens suitable for the multicolumn system. The lens suitable for the multicolumn system needs to have at least a large space in the lens in which an electrostatic deflector having a diameter greater than or equal to several millimeters can be installed. In addition, the lens has to have an electrostatic deflection field capable of being overlapped with a focused magnetic field. This is because these are critical conditions for achieving reduction of beam defocus due to the Coulomb effect and achieving reduction of focus and deflection aberration.
Further, in order to arrange more than several dozens of columns on the 300 millimeter wafer, the lens must have an outer diameter smaller than or equal to 23 millimeters. It is impossible to modify the electron lens employing the permanent magnet having the above-described shape to have an outer diameter smaller than or equal to 23 mm.
As such, there has been no magnetic field-type electromagnetic lens suitable for the multicolumn system. Therefore, it has been impossible to realize a multicolumn electron beam drawing device having more than several dozens of columns with high resolution and low power consumption.
Further, the electron beam drawing device often uses a variable rectangular beam and cell projection (hereinafter abbreviated as CP). The former deflects an electron beam image between the first rectangular aperture and the second rectangular aperture to thereby change the height and width of the rectangular beam as desired. The latter forms, as a CP pattern, a partial pattern included in a cell in a pattern used as an LSI pattern, in a form of a perforated mask on a silicone mask pattern, emits a beam to rectangular portions in a predetermined region on the CP mask in a selective manner, and performs beam molding according to the perforated mask, thereby performing partial collective transfer. Further, the electron beam drawing device may also adopt a multicolumn, multibeam system in which drawing is performed by determining an ON/OFF state of several hundreds to several thousands of individual beams in a single column using bitmap.
The electron beam drawing device which uses only a Gaussian spot beam but does not employ these techniques has not been able to attain sufficient drawing processing capacity even if it is formed as the multicolumn type electron beam drawing device. Therefore, in order to realize a high-speed drawing device, it is essential to form multiple columns while employing the variable rectangular beam, cell projection, and multibeam. There has been demand for realization of such an electron optical system with an electromagnetic lens having an outer diameter smaller than or equal to 23 millimeters.
Patent Document 1 discloses an example of an electron lens employing a permanent magnet (FIG. 5). With this electron lens, reduction of power consumption can be achieved. However, with this electron lens, even if an attempt is made to arrange a plurality of lenses for the multicolumn arrangement, it is impossible to arrange many lenses, and it is therefore impossible to create a high-throughput multibeam type-electron beam drawing device. Further, it is impossible to achieve temperature stability and positional stability of focus and radiation for the individual beams.